Physical/Chemical Properties and Changes
Notes
Physical Property— property that can be observed without changing the identity (make-up) of the
substance (description of the matter)
Examples: mass, volume, weight, density, color, phase, size, texture, smell, taste, hardness, luster,
ductility, malleability, conductivity, viscosity, temperature, boiling point, freezing point, etc.
Density—mass per unit volume
Conductivity—ability to allow heat or electricity to pass through a material
Ductility—ability of some metals to be pulled into wires
Malleability—ability of some metals to be hammered or rolled into thin sheets
Luster—having a shiny appearance or reflecting light
Viscosity—resistance of a liquid to flow
Physical Change—a change that does not affect the make-up of the substance but changes a physical
property, such as size, shape or phase of matter. No new substance is formed because the chemical
identity doesn’t change. When ice melts, the molecules of water become farther apart but the molecules
are still water – 2 hydrogen atoms and 1 oxygen atom (H2O).
Examples: tear paper, dissolve kool-aid, melt ice, condense water vapor, chop an apple, sublimate dry ice,
expand metal by heating, boil alcohol, crush a rock, salt disappearing when mixed with water
Key Words: boil, freeze, melt, condense, vaporize, sublimate, break, split, crack, grind, cut, crush,
bend, dissolve
IMPORTANT: ALL PHASE CHANGES ARE PHYSICAL CHANGES!
Chemical Property—property indicating if a substance is able to change into other substances with new
and different properties. It is a description of a substance’s behavior when it goes through a chemical
change.
Examples: ability to burn (flammable, combustible, or explosive), to corrode, reacts with acid to form
hydrogen, doesn’t react (stable, unreactive, or inert), reacts when exposed to light, can effervesce
(bubble), can tarnish, can heat up or get cold, can produce a precipitate (solid produced from liquids)
(These properties cannot be observed unless a specific change is made to the substance.)
Chemical Change—a change that produces a new substance with different properties. (Atoms are
rearranged.) When a substance goes through a chemical change, some of its physical properties change
but the difference it that the changed physical properties are of a new substance.
For example, when sugar is heated enough, it changes from a sweet, white crystal to a black substance
and a clear liquid. Its physical properties have changed but that is because it is a new substance. Chemical
changes are taking place in our bodies and all around us all the time.
Common Examples:
1. Combustion—chemical change in which a substance combines rapidly with oxygen.
Examples: paper burning, gasoline burning, hydrogen burning, gun powder exploding
2. Corrosion—chemical change in which a metal is gradually changed into a new substance.
Examples: iron rusting, silver tarnishing, copper corroding
3. Cooking Food—involves many chemical reactions.
Examples: baking a cake, cooking an egg
4. Life Processes—involves the many chemical changes that occur in living organisms.
Examples: digestion, respiration, photosynthesis
Key Words: rot, rust, decompose, ferment, grow, decay, corrode, bake, cook, burn
Evidence of Chemical Change
Some chemical changes, like iron rusting, take place slowly and clues may not be observed. Identifying
observed changes as physical or chemical can be tricky because in both cases there are changes in physical
appearance. In general, physical changes are noted for the ease with which they can be reversed. You
need only restore the original conditions and the substance changes back to its original form: Freeze water
to become ice. Frozen ice melts upon warming and turns back into water.
The following are common clues that a chemical change has occurred.
1. Gas is produced—this is usually indicated by bubbles. Bubbles don’t always mean a gas is being
produced (such as air bubbles bubble when something boils).
2. Color or odor change—when a different color or odor appears suddenly, this usually means a new
substance with new properties has formed.
3. Solid formed from 2 liquids—this is called a precipitate. If 2 liquids are combined and a solid
substance suddenly appears that means that a new substance has been formed.
4. Heat released or absorbed—if a substance becomes warmer in temperature even though no heat
is being added that is a clue that a chemical change is occurring. Substances can also get lower in
temperature due to a chemical change.
5. Light produced—sometimes during a chemical change light is given off.